Thus, with the haemorrhage we get ecchymosis, and consequent red staining of the surrounding structures.  As is the case with extravasations of blood elsewhere, the haemoglobin of the escaped corpuscles later undergoes a series of changes, giving rise to a succession of brown, blue, greenish and yellowish coloration.

With the inflammation thereby set up we get swelling of the surrounding bloodvessels, pain from the compression of the swollen structures within the non-yielding hoof, and moistness as a result of the inflammatory exudate.

In a severe case the inflammation is complicated by the presence of pus.

Classification.—­Putting on one side the classification of Lafosse (natural and accidental), as perhaps wanting in correctness, seeing that all are accidental, and disregarding the suggested divisions of Zundel (corn of the sole and corn of the wall) as serving no practical use, we believe, with Girard, that it is better to classify corns according to the changes just described.

Following his system, we shall recognise three forms:  (1) Dry, (2) moist, (3) suppurating.

The dry corn is one in which the injury has fortunately been unattended with excessive inflammatory changes, and where nothing but the coloration imparted to the horn by the extravasated blood remains to indicate what has happened.

The moist corn is that in which a great amount of inflammatory exudate is the most prominent symptom.  It indicates an injury of comparatively recent infliction.

The suppurating corn, as the name indicates, is a corn in which the inflammatory changes are complicated by the presence of pus.

Causes.—­The causes of corns we may consider under two headings—­namely, predisposing and exciting.

Predisposing Causes.—­By the heading of this chapter we have already intimated that corns are due to faulty conformation of the foot.  It is, therefore, merely a description of such shapes of foot as favour their formation that will need mention here.

The wide, flat foot, with low heels, may be first considered.  Here the posterior portions of the sole, those portions between the wall and the bars, fall very largely in the same plane as the wearing surface of the bars and the wall.  As a consequence, these portions of the sole are more prone to receive injury from stones and rough roads and from the pressure of the shoe.

The low heels, too, favour a more than due proportion of the body-weight being thrown on to the posterior parts of the foot.  Two evils, both inclining to the production of corn, result from this.  In the first place, the sensitive structures of the posterior portions of the foot are subjected to undue pressure from above; secondly, the posterior half of the foot, by reason of the extra weight thrown upon it, is exposed